ActiveMasterManager (Apache HBase 1.2.12 API)

java.lang.Object
- org.apache.hadoop.hbase.zookeeper.ZooKeeperListener
- - org.apache.hadoop.hbase.master.ActiveMasterManager

```
@InterfaceAudience.Private
public class ActiveMasterManager
extends ZooKeeperListener
```
Handles everything on master-side related to master election.
Listens and responds to ZooKeeper notifications on the master znode, both nodeCreated and nodeDeleted.
Contains blocking methods which will hold up backup masters, waiting for the active master to fail.
This class is instantiated in the HMaster constructor and the method #blockUntilBecomingActiveMaster() is called to wait until becoming the active master of the cluster.

Field Summary

Fields
Modifier and Type	Field and Description
`(package private) AtomicBoolean`	`clusterHasActiveMaster`
`(package private) AtomicBoolean`	`clusterShutDown`
`private int`	`infoPort`
`private static org.apache.commons.logging.Log`	`LOG`
`private Server`	`master`
`private ServerName`	`sn`

Fields inherited from class org.apache.hadoop.hbase.zookeeper.ZooKeeperListener
watcher

Constructor Summary

Constructors
Constructor and Description

ActiveMasterManager(ZooKeeperWatcher watcher, ServerName sn, Server master)

Constructors
Constructor and Description
`ActiveMasterManager(ZooKeeperWatcher watcher, ServerName sn, Server master)`

Method Summary

Methods
Modifier and Type	Method and Description
`(package private) boolean`	`blockUntilBecomingActiveMaster(int checkInterval, MonitoredTask startupStatus)` Block until becoming the active master.
`(package private) void`	`handle(String path)`
`private void`	`handleMasterNodeChange()` Handle a change in the master node.
`(package private) boolean`	`hasActiveMaster()`
`void`	`nodeCreated(String path)` Called when a new node has been created.
`void`	`nodeDeleted(String path)` Called when a node has been deleted
`void`	`setInfoPort(int infoPort)`
`void`	`stop()`

Methods inherited from class org.apache.hadoop.hbase.zookeeper.ZooKeeperListener
getWatcher, nodeChildrenChanged, nodeDataChanged

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - LOG
```
private static final org.apache.commons.logging.Log LOG
```
  - clusterHasActiveMaster
```
final AtomicBoolean clusterHasActiveMaster
```
  - clusterShutDown
```
final AtomicBoolean clusterShutDown
```
  - sn
```
private final ServerName sn
```
  - infoPort
```
private int infoPort
```
  - master
```
private final Server master
```
- Constructor Detail
  - ActiveMasterManager
```
ActiveMasterManager(ZooKeeperWatcher watcher,
                   ServerName sn,
                   Server master)
```
    Parameters:
    watcher -
    sn - ServerName
    master - In an instance of a Master.
- Method Detail
  - setInfoPort
```
public void setInfoPort(int infoPort)
```
  - nodeCreated
```
public void nodeCreated(String path)
```
    Description copied from class: ZooKeeperListener
    
    Called when a new node has been created.
    
    Overrides:
    
    nodeCreated in class ZooKeeperListener
    
    Parameters:
    path - full path of the new node
  - nodeDeleted
```
public void nodeDeleted(String path)
```
    Description copied from class: ZooKeeperListener
    
    Called when a node has been deleted
    
    Overrides:
    
    nodeDeleted in class ZooKeeperListener
    
    Parameters:
    path - full path of the deleted node
  - handle
```
void handle(String path)
```
  - handleMasterNodeChange
```
private void handleMasterNodeChange()
```
    Handle a change in the master node. Doesn't matter whether this was called from a nodeCreated or nodeDeleted event because there are no guarantees that the current state of the master node matches the event at the time of our next ZK request.
    Uses the watchAndCheckExists method which watches the master address node regardless of whether it exists or not. If it does exist (there is an active master), it returns true. Otherwise it returns false.
    A watcher is set which guarantees that this method will get called again if there is another change in the master node.
  - blockUntilBecomingActiveMaster
```
boolean blockUntilBecomingActiveMaster(int checkInterval,
                                     MonitoredTask startupStatus)
```
    Block until becoming the active master. Method blocks until there is not another active master and our attempt to become the new active master is successful. This also makes sure that we are watching the master znode so will be notified if another master dies.
    
    Parameters:
    checkInterval - the interval to check if the master is stopped
    startupStatus - the monitor status to track the progress
    
    Returns:
    True if no issue becoming active master else false if another master was running or if some other problem (zookeeper, stop flag has been set on this Master)
  - hasActiveMaster
```
boolean hasActiveMaster()
```
    Returns:
    True if cluster has an active master.
  - stop
```
public void stop()
```

Class ActiveMasterManager

Field Summary

Fields inherited from class org.apache.hadoop.hbase.zookeeper.ZooKeeperListener

Constructor Summary

Method Summary

Methods inherited from class org.apache.hadoop.hbase.zookeeper.ZooKeeperListener

Methods inherited from class java.lang.Object

Field Detail

LOG

clusterHasActiveMaster

clusterShutDown

sn

infoPort

master

Constructor Detail

ActiveMasterManager

Method Detail

setInfoPort

nodeCreated

nodeDeleted

handle

handleMasterNodeChange

blockUntilBecomingActiveMaster

hasActiveMaster

stop